In Peyton Place, Parkins received lead billing for her role as small-town bad girl Betty Anderson. As initially conceived, the character was scheduled to die in a car crash six weeks into the season, but audience reaction to Parkins was overwhelmingly favorable, and it was decided to keep her in the story line. In a late 1965 interview, the actress said about her role:

I'm lucky in the role I have. Mine was the big story when the series started off. I haven't had much to do lately, but when I do have scenes, they are important to the plot. You might say I'm the salt and pepper in the stew.[3]

She was the only female star to remain with the series through its entire run (1964–1969). In 1966, she was nominated for an Emmy Award as Best Actress in a Lead Role in a Dramatic Series, but lost to Barbara Stanwyck for The Big Valley. About losing the award on her 24th birthday, Parkins told the press:

I was hurt, but if I had to lose I was glad it was to Barbara Stanwyck, who is a grand lady and fine actress. I would have hated to lose to Anne Francis. I don't care much for her work. A woman should be feminine and not go around hitting people with judo chops the way she does in that Honey West show.[4]

Eventually shedding her "other side of the tracks" image, Betty endured many of the trials and tribulations of soap-opera life. The character achieved such popularity that when the show ended its run, producer Paul Monash developed a spin-off series, The Girl from Peyton Place, for Parkins. However, when co-star Ryan O'Neal, who played her husband, declined to participate, the project was shelved. Nevertheless, Parkins insisted she often felt very insecure on the set, saying

Sometimes I think I hold myself in too tightly. I would watch Lee Grant do those wild things when she played Stella Chernak and think I should try something like that, but when I did I was pathetic. I'm very critical of what I see of myself, but I did get an Emmy nomination, didn't I?.[4]

In Valley of the Dolls, Parkins played Anne Welles, the naive small-town girl described as "the good girl with a million-dollar face and all the bad breaks"—a character based on author Susann. The film was trashed by the critics, although Parkins was one of the few to emerge unscathed. However, the movie was a huge commercial success and eventually became a campy cult classic. "Jackie was... taken with Barbara, who she felt resembled an earlier Jackie Susann, dark and intense and with a distinctive voice."[5]

I get calls now, from young actors I used to have crushes on. They'll ask me out now, when they wouldn't a year ago. And I love to say "No" to them. I'd have liked it once, but now I don't need them.[7]

Parkins posed for nude pictorials in the May 1967, February 1970 and May 1976 editions of Playboy magazine. She spent most of the mid-1970s appearing on American television in several miniseries, including Jennie: Lady Randolph Churchill with Lee Remick, Captains and the Kings alongside her Dolls co-star, Patty Duke, and The Testimony of Two Men with William Shatner. She also appeared in guest spots on Fantasy Island, The Love Boat, Hotel, and Vega$.

In the late 1970s, Parkins moved to France and married, and in the late 1980s, she adopted her only child, daughter Christina.

In the 1980s, she continued to work in television movies, including To Catch a King, in which she portrayed the Duchess of Windsor, and opposite Sharon Stone in The Calendar Girl Murders. She also auditioned for the title role in the James Bond film Octopussy (1983), but lost to Maud Adams. She returned to the role of Betty Anderson in Peyton Place: The Next Generation (1985), a one-shot sequel to her popular series.

In 1991, she starred in a Canadian mystery series entitled Scene of the Crime, then spent most of the remainder of the decade in semiretirement. She emerged in the late 1990s to participate in two Susann-inspired projects, the biography Scandalous Me and a segment of the Lifetime series Intimate Portrait. In 1995, she was chosen by Empire magazine as number 81 on their list of 100 Sexiest Stars in film history.[citation needed]